The present disclosure relates to railroad freight cars and, more particularly, to hopper cars having through center sills.
To accommodate the widely varying types of cargo that may travel over a railroad, rail cars of many different designs are manufactured, and in some instances a rail car will be specially designed to carry one specific type of cargo. One type of cargo that is often transported via railroad is cargo having bulk fluid properties, meaning commodities that, in bulk, exhibit fluid-like behavior. Examples of such commodities are grain, nuts, and cement, etc. Such bulk fluid cargo is typically transported in a hopper car that is specially designed to carry cargo having bulk fluid properties.
A hopper car usually includes one or more cargo-carrying bins, called cargo wells, which may be filled with grain or other bulk fluid cargo. The cargo is typically poured into the hopper car from the top and discharged from the bottom, through a respective discharge outlet at the bottom of each cargo well. Each discharge outlet is selectively closeable to permit the loading and transporting of the cargo. A discharge outlet is usually located approximately at the center of the cargo well that it empties. When the discharge outlet is opened, the bulk fluid cargo flows from the hopper car. To facilitate the flow of cargo towards these outlets while a hopper car is being emptied, each cargo well will usually include at least one pair of opposed slope sheets, that are slanted downwardly and inwardly towards the respective outlet at the center of the cargo well.
One specific type of hopper car is a through center sill hopper car. A hopper car, like other rail cars, is structurally supported by an undercarriage that includes a center sill extending longitudinally along the center line of the hopper car. A through center sill hopper car has a center sill that runs through the cargo wells of the hopper car, and the cargo in each cargo well thus can surround the center sill. In order to facilitate the flow of cargo around the center sill when the cargo is unloaded, the portion of a center sill within a cargo well is typically covered by a tent-like hood with sloping upper surfaces, so that the bulk fluid cargo does not collect on top of the center sill when the hopper car empties.
The center sill is a primary load-bearing structural member of the hopper car, extending longitudinally between and interconnecting stub sills at the ends of the car to complete a center sill assembly. The center sill is thus the longitudinally central portion of a center sill assembly. The center sill must be of a sufficiently sturdy construction to withstand not only the substantial standing weight of both the hopper car and the cargo it carries, but also the buff and draft forces and various bending and rotational stresses that are applied to the hopper car as it moves along a railroad track as part of a train.
In the past, a center sill was typically constructed of two pairs of opposed, parallel elongate pieces of steel plate or other similarly rigid material, joined as an elongate box beam. These individual members are usually welded together along the right-angle intersections between adjacent members, and are typically fashioned of steel ½-inch thick, or thicker, so as to withstand the aforementioned loads and stresses. Often, the center sill is further reinforced by a plurality of gussets or other reinforcements inside the center sill.
Unfortunately, the size of a traditional center sill previously has substantially added to the weight of the hopper car, and its construction as described above has required a substantial amount of time and labor by skilled welders. What is desired, therefore, is a new center sill structure that is lighter in weight than center sills in existing hopper cars of similar load capacity, and that can be manufactured more easily and economically, yet is able to durably withstand the same loads and stresses as do the center sills of existing hopper cars of similar carrying capacity.